Epsom salt (magnesium sulfate) is a common mineral compound used by gardeners to supplement citrus trees. It delivers magnesium and sulfur, two macronutrients required for healthy plant function. Applying Epsom salt primarily addresses magnesium deficiency, providing a rapid nutritional boost when specific symptoms are observed.
Recognizing the Need for Magnesium and Sulfur
Magnesium deficiency in citrus trees first appears on older, mature leaves. Magnesium is a mobile nutrient, meaning the tree moves it from older foliage to supply new growth or developing fruit. This internal reallocation causes older leaves to show the deficiency first, distinguishing it from other nutrient issues that appear on new leaves.
The characteristic sign of insufficient magnesium is chlorosis, or yellowing, between the leaf veins. The discoloration starts near the base and moves outward, leaving a distinct inverted V-shape or “Christmas tree” pattern of green along the midrib and main veins. Severe deficiency can cause the entire leaf to yellow, turn bronze, and drop prematurely, especially under heavy fruit load.
Magnesium is essential for photosynthesis; inadequate levels reduce the tree’s vigor and fruit quality. Sulfur, the other component of Epsom salt, is a macronutrient involved in protein and enzyme synthesis. However, sulfur deficiency symptoms usually appear on new growth first. Therefore, the inverted V pattern on older leaves is the primary indicator that Epsom salt treatment is appropriate.
Recommended Application Methods and Dosages
Epsom salt can be applied as a rapid-acting foliar spray or a slower, long-term soil drench or broadcast application. Dosages differ significantly, and the choice depends on the deficiency severity and desired speed of correction.
Foliar Spray (Quick Fix)
Foliar spray is the fastest way to deliver magnesium directly into the tree’s system, as leaves absorb the nutrient more readily than roots. To prepare the solution, dissolve 1 to 2 tablespoons of Epsom salt in one gallon of water. Ensure the crystals are completely dissolved before application to prevent leaf burn.
Spray the solution directly onto the leaves, fully covering both the top and bottom surfaces. Apply in the early morning or late afternoon when temperatures are cooler for maximum absorption. Repeat the foliar application every two to four weeks until deficiency symptoms subside.
Soil Drench/Broadcast (Long-Term Treatment)
For sustained, long-term correction of a soil-based magnesium deficit, a soil application is recommended. The amount used depends on the tree’s size and whether it is planted in the ground or a container.
For small container-grown trees, dissolve one tablespoon of Epsom salt in one gallon of water and apply it as a soil drench around the base of the plant.
For in-ground trees, the dosage is significantly higher and is measured in cups or pounds applied annually. A young tree (under five feet) requires 1/4 to 1/2 cup of dry Epsom salt spread around the drip line. A mature, large citrus tree can tolerate 1 to 2 pounds (2 to 4 standard cups) spread evenly beneath the canopy.
Broadcast the salt evenly over the soil surface, starting a few inches away from the trunk and extending out to the drip line. Lightly rake the salt into the top inch of soil and water thoroughly to dissolve the crystals and move the magnesium down into the root zone. Apply once or twice per year, usually in the spring and fall, to maintain healthy magnesium levels.
When Epsom Salt is Not the Solution
Applying Epsom salt without confirming the specific need can be counterproductive. Excessive magnesium interferes with the uptake of other essential nutrients, most notably calcium. If the magnesium-to-calcium balance in the soil is skewed, the tree may suffer from an induced calcium deficiency, negatively affecting fruit structure and overall plant development.
Epsom salt does not solve underlying soil pH problems. Citrus trees thrive in slightly acidic to neutral soil. If the soil is too alkaline, it can “lock up” iron and zinc, causing deficiency symptoms sometimes confused with magnesium issues. Applying Epsom salt does not significantly change the soil pH, meaning the root cause of nutrient unavailability remains unaddressed.
Epsom salt is also ineffective for deficiencies of other nutrients, such as nitrogen, iron, or zinc. Iron and zinc deficiencies affect the newest growth first, causing yellowing on young leaves, which clearly distinguishes them from magnesium deficiency. Using Epsom salt in these cases delays the application of the correct treatment.